_large molecule drugs_ — **protein-based therapeutics known as biologics** — are made by living cells. They must be administered via injection because they will be destroyed by digestive enzymes in the gastrointestinal tract if given orally. Their large size, anywhere from **50 to 1,000 times larger** than a typical small molecule drug, makes it impossible for them to penetrate cells. On the flip side, large molecules are highly specific for their target — typically a cell-surface receptor on the outside of the cell.